1. Field of the Invention
This invention relates to a current limiting contactor and more particularly, it pertains to a cantilevered single break current limiting contactor.
2. Description of the Prior Art
Contactors, fuses, circuit breakers, and magnetic and thermal overload relays are all part of industrial motor control systems. The essential functions of industrial motor control are starting, stopping, speed regulation, and protection of electric motors. Contactors are devices, generally magnetically activated, for repeatedly establishing and interrupting an electrical power circuit. Usually contactors must be able to interrupt up to six times a full load current. However, they do not have any built-in intelligence to sense and react to protect themselves against severe overloads or short circuits. Fuses are generally provided for motor circuits for overload or short circuit conditions, But, the current rating of the fuse must be considerably higher than the current rating of the motor or the fuse will blow when the motor is started. As a result, fuses do not provide adequate overload protection for motors. Furthermore, contactors must withstand severe overloads in short circuit currents while the fuse is melting. This generally results in welded contacts as well as a blown fuse. Both the contacts and the fuse must be replaced before the equipment can be used again.
Current limiting can be accomplished by generating a rapid rise in current voltage up to the system voltage. When the arc voltage has reached or exceeded the system voltage, the current will peak and be forced to zero before the first normal current zero. The peak current and the I.sup.2 t let through are therefore direct functions of how rapidly the arc voltage is generated. A rapid rise in arc voltage can be accomplished by separating contacts rapidly and by stretching the arc with a magnetic field.